1. Field of the Invention
The present invention relates to an arrangement for adjusting the roll gap or the rolling force in rolling mill stands, particularly in strip rolling mill stands for hot or cold rolling. The arrangement includes at least two hydraulic adjusting cylinders which act through chucks, and possibly through intermediately mounted back-up rolls, from both sides on a work roll to be adjusted.
2. Description of the Related Art
In rolling mill stands for rolling steel and non-ferrous metals, it is known in the art to adjust the work rolls, i.e., usually the upper roll and the lower roll, by means of hydraulic adjusting cylinders. The adjustment results in a change of the width of the roll gap and in a change of the rolling force. Particularly in strip rolling mill stands for hot or cold rolling, hydraulic adjusting cylinders having almost completely replaced the conventional adjustment by means of threaded spindles.
In cold rolling mill stands, the rolling forces range from several hundred tons to several thousand tons. For example, in skin pass rolling mill stands or temper pass rolling mill stands, the rolling forces range from about 100 tons to about 1500 tons, depending on the dimensions of the strip and the strength of the material. The rolling forces of this magnitude must be transmitted from always two hydraulic adjusting cylinders through the chocks to the work roll. This means that the work rolls do not only have to be adjusted but the adjustment of the roll gap must be maintained in this position. The hydraulic adjusting cylinders are quickly adjusted by means of a low liquid pressure, while a high pressure pump produces the rolling forces.
The pressure control is effected by means of hydraulic power-assisted valves. Such power-assisted valves operate with a maximum pressure of about 250 bar and with a controlling accuracy of about .+-. 1.0 bar. The controlling deviations are almost constant over the entire pressure range. The controlling range of the rolling force for a rolling mill stand is approximately 1 : 15 to 1 : 20. This means for a rolling mill stand with a rolling force range of, for example, 100 tons to 1500 tons and a maximum pressure of 250 bar, a controlling deviation from the rolling force of .+-. 6 tons. In the case of a 100 ton nominal rolling force, this means a controlling deviation of .+-. 6 tons = 12 tons = 12%, while in the case of a nominal rolling force of 1500 tons this means only .+-. 6 tons = 12 tons = 0.8%. Accordingly, the controlling deviations are significantly greater in the lower rolling force range than in the upper rolling force range. When rolling metal strip, this leads to corresponding deviations of the thickness of the strip over the length of the strip. In temper pass rolling mill stands, in which in addition to a slight reduction in thickness primarily a certain surface conditioning, for example, a predetermined roughness is to be obtained, such rolling force variations lead to different roughness and differences in the strip thickness over the length of the strip at spacings which correspond to the controlling frequency of the power-assisted valves. Such deviations lead to failures during the subsequent processing of the metal strip, for example, during deep drawing, coating or the like. If such rolling mill stands are used in processing trains such as continuous strip pickling trains, annealing trains, coating trains, or the like, it is necessary to use several rolling mill stands with different rolling force ranges.